I haven't tried them but know several farmers who use tillage radishes as part of a cover crop mix. The only issues besides price seem to be they need to go in relatively early in our area so they are better behind corn than soybeans and they aren't very good in really wet soil.
That's 2 of the purposes. In addition to reducing soil erosion and weed control they also break up the ground (down as much as 4 feet) so water and nutrients get taken down below the surface and most radishes die after freeze and rot in the ground adding organic material and beneficial bacteria/fungi which end up enriching the soil.I'm as far from a farmer as one can be but I walk a lot of farmland chasing pheasants and quail. I have come across this radish cover crop a few times. If I understand the strategy, farmers use it as a cover crop when they were unable to plant their normal crop (corn or soybeans) due to wet soil too late into the season. They just let it go then till it in come spring. If they don't plant something too many weeds take root and it helps control erosion.
Does that sound right? More curious than anything.
When radishes (tillage radishes) first became popular my seed salesman friend got several complaints from the public (farmers neighbors) about smelling a persistent gas leak, yes they do smell.I the only time I have seen them used here was about 8 years ago, we had 18 inches of snow in May!!!!! about half of the crops never even got planted. The government paid out a bunch of money to try and make the farmers somewhat whole, and one of the requirements was that they had to plant a cover crop. Many put radishes in. 1000's of acres. In the fall when they started dying and rotting, they stunk to high heaven The deer were sure happy!